Jeffrey H. Bowles

Interpretation of hyperspectral remote-sensing imagery by spectrum matching and look-up tables

A spectrum-matching and look-up-table (LUT) methodology has been developed and evaluated to extract environmental information from remotely sensed hyperspectral imagery. The LUT methodology works as follows. First, a database of remote-sensing reflectance (Rrs) spectra corresponding to various water depths, bottom reflectance spectra, and water-column inherent optical properties (IOPs) is constructed using a special version of the HydroLight radiative transfer numerical model. Second, the measured Rrs spectrum for a particular image pixel is compared with each spectrum in the database, and the closest match to the image spectrum is found using a least-squares minimization. The environmental conditions in nature are then assumed to be the same as the input conditions that generated the closest matching HydroLight-generated database spectrum. The LUT methodology has been evaluated by application to an Ocean Portable Hyperspectral Imaging Low-Light Spectrometer image acquired near Lee Stocking Island, Bahamas, on 17 May 2000. The LUT-retrieved bottom depths were on average within 5% and 0.5 m of independently obtained acoustic depths. The LUT-retrieved bottom classification was in qualitative agreement with diver and video spot classification of bottom types, and the LUT-retrieved IOPs were consistent with IOPs measured at nearby times and locations.

Ocean PHILLS hyperspectral imager: design, characterization, and calibration

The Ocean Portable Hyperspectral Imager for Low-Light Spectroscopy (Ocean PHILLS) is a hyperspectral imager specifically designed for imaging the coastal ocean. It uses a thinned, backsideilluminated CCD for high sensitivity and an all-reflective spectrograph with a convex grating in an Offner configuration to produce a nearly distortionfree image. The sensor, which was constructed entirely from commercially available components, has been successfully deployed during several oceanographic experiments in 1999-2001. Here we describe the instrument design and present the results of laboratory characterization and calibration. We also present examples of remote-sensing reflectance data obtained from the LEO-15 site in New Jersey that agrees well with ground-truth measurements.

Use of filter vectors in hyperspectral data analysis

We report recent progress using a filter vector technique to analyze the data from a hyperspectral image. The filter vector technique finds the optimal filter vectors for demixing the complex patterns found in the hyperspectral image. The method has the potential to be implemented in real time since it is fully parallel. Computation of the filter vectors for a given family of known species vectors is fast and direct and improved algorithms for developing of the algorithm which may be updated as conditions change is possible. Advantages of using the filter vector techniques over the technique of pattern matching will be discussed. The portable hyperspectral images for low light spectroscopy (PHILLS) instrument has been used on a number of depolyments in the last year. Typically, the instrument files on the Naval Research Laboratorys P-3 Orion aircraft. Currently, the PHILLS instrument records over 1000 wavelength bands between UV and near IR. Results from a number of deployment and test situations is shown.

Velocity‐shear‐driven ion‐cyclotron waves and associated transverse ion heating

Recent sounding rocket experiments, such as SCIFER, AMICIST, and ARCS-4, and satellite data from FAST, Freja, DE-2, and HILAT, provide compelling evidence of a correlation between small-scale spatial plasma inhomogeneities, broadband low-frequency waves, and transversely heated ions. These naturally arising, localized inhomogeneities can lead to sheared cross-magnetic-field plasma flows, a situation that has been shown to have potential for instability growth. Experiments performed in the Naval Research Laboratorys Space Physics Simulation Chamber demonstrate that broadband waves in the ion-cyclotron frequency range can be driven solely by a transverse, localized electric field, without the dissipation of a field-aligned current. Significant perpendicular ion energization resulting from these waves has been measured. Detailed comparisons with both theoretical predictions and space observations of electrostatic waves found in the presence of sheared cross-magnetic-field plasma flow are made.

Cross-Scale Patterns in Shrub Thicket Dynamics in the Virginia Barrier Complex

A bstractTo interpret broad-scale erosion and accretion patterns and the expansion and contraction of shrub thickets in response to sea level rise for a coastal barrier system, we examined the fine-scale processes of shrub recruitment and mortality within the context of the influence of ocean current and sediment transport processes on variations in island size and location. We focused on Myrica cerifera shrub thickets, the dominant woody community on most barrier islands along the coastline of the southeastern USA. Observations suggest that M. cerifera, a salt-intolerant species, is increasing in cover throughout the Virginia barrier islands, yet rising sea level in response to climate change is increasing erosion and reducing island area. Our objective was to explain this apparent paradox using pattern–process relationships across a range of scales with a focus on ocean currents and sediment transport interacting with island characteristics at intermediate scales. Multi-decadal comparisons across scales showed a complex pattern. At the scale of the entire Virginia barrier complex, modest decreases in upland area were accompanied by large increases in shrub area. Responses were more variable for individual islands, reflecting inter-island variations in erosion and accretion due to differences in sediment transport via ocean currents. Several islands underwent dramatic shrub expansion. Only for within-island responses were there similarities in the pattern of change, with a lag-phase after initial shrub colonization followed by development of linear, closed canopy thickets. Understanding the fine-scale processes of shrub seedling establishment and thicket development, in conjunction with the influence of ocean currents and sediment transport, provides a framework for interpreting island accretion and erosion patterns and subsequent effects on shrub thicket expansion or contraction across scales of time and space.

Perpendicular ion heating by velocity‐shear‐driven waves

Perpendicular ion heating resulting from velocity-shear-driven ion-cyclotron waves has been measured for the first time. The experiment was performed in the Naval Research Laboratorys Space Physics Simulation Chamber (SPSC) under plasma conditions approaching those in the natural space environment. Sheared cross-field flow is induced by a controllable, inhomogeneous, transverse, DC electric field (LE ∼ (1–2)ρi) created without drawing significant levels of magnetic-field aligned current. Mode frequency data suggest that the most efficient heating occurs when the Doppler shifted frequency in the ion frame is located near a harmonic of the ion-cyclotron frequency.

Bathymetric Retrieval From Hyperspectral Imagery Using Manifold Coordinate Representations

In this paper, we examine the accuracy of manifold coordinate representations as a reduced representation of a hyperspectral imagery (HSI) lookup table (LUT) for bathymetry retrieval. We also explore on a more limited basis the potential for using these coordinates for modeling other in water properties. Manifold coordinates are chosen because they are a data-driven intrinsic set of coordinates, which naturally parameterize nonlinearities that are present in HSI of water scenes. The approach is based on the extraction of a reduced dimensionality representation in manifold coordinates of a sufficiently large representative set of HSI. The manifold coordinates are derived from a scalable version of the isometric mapping algorithm. In the present and in our earlier works, these coordinates were used to establish an interpolating LUT for bathymetric retrieval by associating the representative data with ground truth data, in this case from a Light Detection and Ranging (LIDAR) estimate in the representative area. While not the focus of the present paper, the compression of LUTs could also be applied, in principle, to LUTs generated by forward radiative transfer models, and some preliminary work in this regard confirms the potential utility for this application. In this paper, we analyze the approach using data acquired by the Portable Hyperspectral Imager for Low-Light Spectroscopy (PHILLS) hyperspectral camera over the Indian River Lagoon, Florida, in 2004. Within a few months of the PHILLS overflights, Scanning Hydrographic Operational Airborne LIDAR Survey LIDAR data were obtained for a portion of this study area, principally covering the beach zone and, in some instances, portions of contiguous river channels. Results demonstrate that significant compression of the LUTs is possible with little loss in retrieval accuracy.

Impact of Signal-to-Noise Ratio in a Hyperspectral Sensor on the Accuracy of Biophysical Parameter Estimation in Case II Waters

Errors in the estimated constituent concentrations in optically complex waters due solely to sensor noise in a spaceborne hyperspectral sensor can be as high as 80%. The goal of this work is to elucidate the effect of signal-to-noise ratio (SNR) on the accuracy of retrieved constituent concentrations. Large variations in the magnitude and spectral shape of the reflectances from coastal waters complicate the impact of SNR on the accuracy of estimation. Due to the low reflectance of water, the actual SNR encountered for a water target is usually quite lower than the prescribed SNR. The low SNR can be a significant source of error in the estimated constituent concentrations. Simulated and measured at-surface reflectances were used in this study. A radiative transfer code, Tafkaa, was used to propagate the at-surface reflectances up and down through the atmosphere. A sensor noise model based on that of the spaceborne hyperspectral sensor HICO was applied to the at-sensor radiances. Concentrations of chlorophyll-a, colored dissolved organic matter, and total suspended solids were estimated using an optimized error minimization approach and a few semi-analytical algorithms. Improving the SNR by reasonably modifying the sensor design can reduce estimation uncertainties by 10% or more.

Comparison of low-cost hyperspectral sensors

Recent advances in large format detector arrays and holographic diffraction gratings have made possible the development of imaging spectrographs with high sensitivity and resolution, at relatively low component cost. Several airborne instruments have been built for the visible and near IR spectral band with 10-nm resolution, and SNR of 200:1. Three instruments are compared, an all-reflective spectrography using a convex grating in an Offner configuration, and two off-the-shelf transmission grating spectrographs using volume holograms. The camera is a 1024 X 1024 frame transfer, back-thinned CCD, with four taps for obtaining high frame rates. Performance and scan data is presented and compared to the design for image quality, distortion, and throughput.

Hyperspectral analysis and target detection system for the Adaptive Spectral Reconnaissance Program (ASRP)

A multiprocessor version of the ORASIS hyperspectral analysis program has been implemented in support of the ASRP. In brief, the long-term technical objectives of the ASRP are to demonstrate the feasibility and military utility of real-time target detection from uncrewed air vehicles using hyperspectral data. This paper presents a preliminary assessment of ORASIS performance and describes the ORASIS development effort designed to meet the ASRP goals. Real-time performance of the analysis program and its potential effectiveness as a target detection method are demonstrated.